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<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script>
        console.log(123 && 456); //456
        console.log(0 && 456); //0
        console.log(0 && 0 + 2 && 4 + 5); //0
        console.log('' && 1 + 2 && 456); // ''
        console.log(123 || 456); //123
        console.log(123 || 456 || 123 + 456); //123
        console.log(0 || 123 || 456+123); //123
        var num = 0;
        console.log(123 || num++);  //123
        console.log(num);  //0
    </script>
</head>

<body>

</body>

</html>